Method, apparatus, and processes for producing potable water utilizing reverse osmosis at ocean depth in combination with shipboard moisture dehumidification

ABSTRACT

Devices and methods for producing purified water. The device includes a reverse osmosis subsystem, a dehumidification subsystem and a purified water storage tank fluidly coupled to the subsystems such that purified water produced by each can be locally stored. A vehicular platform, such as a ship, can be used to locate the device adjacent a supply of saline water and humid air. A saline water inlet, membrane and purified water outlet cooperate in the reverse osmosis subsystem to allow preferential passage of water relative to salt in a saline water supply, while the dehumidification subsystem includes a heat exchanger that extracts moisture from the ambient humid air. Purified water produced by each of the subsystems can be used as a potable water source. When used in conjunction with a ship, part or all of the reverse osmosis subsystem can be submersed to a depth sufficient to generate a hydrostatic pressure that is in turn sufficient to passively operate the reverse osmosis membrane such that additional pressurizing equipment, such as a pump, is not needed. Furthermore, the temperature of the water purified by the reverse osmosis subsystem may be low enough to be used as a condensing agent for the ambient humid air passing through the dehumidification subsystem.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/481,082, filed Jun. 9, 2009 now U.S. Pat. No. 7,901,580 (nowallowed).

BACKGROUND OF THE INVENTION

The present invention relates generally to an apparatus and process forproducing potable water using a combination of reverse osmosis (RO) anddehumidification, and more particularly to a combination of shipboard ROand dehumidification to extract and store potable water from a saltwatersupply.

A concomitant to an increase in global population is the need forpotable water for human consumption, as well as for industrial,agricultural and other uses. Because the availability of freshwatersupplies is limited by size, cleanliness and lack of accessibility,there exists a need for creating potable water from other sources.Stewardship measures such as conservation and reuse, while laudable,will not in and of themselves be sufficient to meet the increase inworldwide water demand.

The world's seas and oceans are the most notable source of yetrelatively untapped water. Unfortunately, their high saline contentprecludes their use as a supply of potable water. Traditionally, thedesalination of sea water is accomplished using land-based facilities,typically relying upon either active evaporative or reverse osmosis (RO)techniques. In the former, the salty water is first vaporized, thencondensed in such a way as to isolate the relatively salt-freedistillate. Active evaporation is expensive, requiring vast amounts ofenergy (typically in the form of a combustible heat supply).

The latter approach involves using high pressure to force the saltywater through a membrane that is relatively impermeable to salt ions orother contaminants, thereby allowing a more pure form of the water topass through the membrane. Traditional RO approaches typically involvesome amount of pre-treatment, filtration, and final treating.Pre-treatment may include screen and physical filtration (often withcarbon filters), as well as chemical pre-treatment, which may includescaling and biological prevention. From the pre-treatment, the water isthen sent to the membrane for desalination and filtration. Membranesused in RO for the desalination of sea water come in four primaryphysical structures. These are spiral, tubular, plate and frame, andhollow fiber systems. Spiral systems are made up of two concentric tubes(typically about 8″ and 2″ in diameter) the length of which is dependenton system pressure and the concentration of solids in the raw water. Theactual membrane is typically a flat sheet with one end open to the waterand the other ending in the smaller of the two tubes. The membrane isthen spiraled around the inner tube and placed inside the larger tube.Raw water enters the larger tube under pressure. Pure water then entersinto the membrane and flows along the spiral until it is released intothe inner tube where it is transported for final treatment. Concentratedbrine then flows out the open end of the larger tube. Tubular and hollowfiber systems are essentially the same design differing only in theirrelative size. In both cases, membranes are cylindrical fibers or tubesplaced in an outer tube. The outer tube is filled with pressurized rawwater. The pure filtered water enters the tubes or fibers and istransported down these to final treatment. Concentrated brine flows outof the open end of the outer tube. Plate and frame systems involve aflat surface membrane with the filtering side exposed to raw water andthe reverse exposed to the product water chamber. Pressurized raw wateris exposed to the filter. The filtered pure water moves through into thecollection chamber for processing. Final treatment involves thebalancing and treating of mineral content in the water, as well asbalancing the acidity of the water. Additionally, ultraviolet (UV) raysor chlorination can be employed to control future biological andpathogenic contamination.

As with the active evaporation process discussed above, land-based ROfacilities suffer from various shortcomings. For example, because ROfacilities generate significant quantities of dissolved solids andrelated effluent, release of such byproducts could be harmful ifreintroduced in localized, concentrated form into the water supply fromwhich it was derived. Such localized release of effluent wouldeventually cause the water being taken into the system to becomeconcentrated enough that it can impact the performance of the RO systemmembranes. To ensure a relatively non-fouled RO water intake, thefacility would need to be situated remotely from the point of effluentdischarge. Similarly for evaporative systems, local nuisance concernsmay mean that there are significant costs associated with keeping thefacility at a suitable distance from population centers. In eithersituation, the solution tends to be cost-prohibitive.

One way to avoid the problems associated with land-based desalination(in particular, land-based RO desalination) is to use a shipboard ROsystem. In a conventional form, the high pressure requirements aresatisfied by mechanical pumps. Such systems, while operationallysuitable, are expensive, require significant amounts of energyconsumption, and take up precious shipboard space. As an alternative, ithas been reported that the necessary pressure differential can beachieved hydrostatically if the RO unit is submersed to a sufficientdistance (for example, many hundreds of meters) beneath the oceansurface. Despite improvements in energy efficiency made possible by sucha system, there remains a desire to increase the quality of potablewater from ship-based platforms over that provided by these or relatedRO systems, as well as a desire to reduce the impact of RO-baseddesalination on the local environment from which the water wasextracted.

BRIEF SUMMARY OF THE INVENTION

These needs are met by the present invention, where in accordance with afirst aspect of the present invention, features of a system made up ofeach RO and evaporative components work together for water desalination.The system includes an RO subsystem, a dehumidification subsystem, atleast one purified water storage tank and a vehicular platform ontowhich the RO and dehumidification subsystems and the purified waterstorage tank (or tanks) are mounted. The tank is fluidly coupled to theRO subsystem and the dehumidification subsystem such that purified waterproduced by each is stored in the tank. The RO subsystem includes asaline water inlet, a purified water outlet fluidly downstream of theinlet and between them an RO membrane that acts as a filter for saltsand other contaminants by allowing passage of water through it whileinhibiting the passage of such undesirable features present in a salinewater supply. The dehumidification subsystem is a passive system, whichdiffers from an active system in that it doesn't require a combustion orrelated source in order to achieve an appreciable measure of separationof the airborne salts or related minerals or impurities from a humidambient air supply. In such a passive approach, the system uses waterpurified by the RO subsystem to act as a coolant to condense at leastsome of the water contained in this ambient air.

Optionally, the vehicle can include any mechanized equipment used toconvey the purified water. In a preferred form, the vehicle is awatercraft, such as a ship, boat, submarine or the like. In anotheroption, the RO subsystem extracts potable water from the saline watersupply by passive means, rather than through active means, such aspumping. In the present context, passive means could result fromdifferences in hydrostatic pressure between the inlet and the outlet,movement of the inlet to force higher quantities of flow therein orother means that don't rely on pumps or other such devices. In apreferred form, the ship is large enough to function as a storage ofboth the system and significant quantities of purified water. In onesuch form, the ship weighs at least 40,000 tons, although any midsizetanker (i.e., one big enough to contain multiple RO units in theirdocking stations and hold an appropriately-sized dehumidification unit)would be acceptable. While larger ships could be used in conjunctionwith the present invention, their use must be able to operate within theconstraints of the ports into which they would need to navigate.

The watercraft further may include pipes, pumps, valves and relatedfluid handling equipment to facilitate conveying the purified water to atank on another watercraft, the land or elsewhere. In yet anotheroption, the dehumidification subsystem is positionable relative to theambient air supply such that the amount of the ambient air thatinteracts with the dehumidification subsystem is maximized. The ROsubsystem may more particularly include a container and an RO unitfluidly connected to the container. In one form, the purified waterproduced at the membrane can be at least temporarily stored in thecontainer, for example, at least until fluid communication can beestablished between the container and one or more of the onboard storagetanks, or until such time as the purified water in the container can beused by the dehumidification subsystem to help condense water vaporpresent in the ambient air. As stated above, the one or more storagetanks can be made up of numerous such tanks fluidly coupled to andspaced from one another. For example, by placing them at select remotelocations in the ship (such as at opposing sides or corners thereof),the tanks can be used as a balancing system, where the purified waterstored in the numerous tanks can be allocated in such a way to promotehydrostatic balancing within the ship.

In another option, the dehumidification subsystem may include a screenor related porous device through which a breeze, the wind or the likecan carry the ambient air. Porous members located in thedehumidification subsystem allow the wicking of water (in the form ofhumidity in the ambient air) into a flowpath that drains into anappropriate trough or related sluice. Motors, winches or the like can beused to reposition the screen of the dehumidification subsystem so thatit best aligns with the prevailing winds to take best advantage of thesystem's evaporative capabilities.

The system may further include a positioning mechanism that permitsmovement of at least the RO subsystem through various depths of thesaline water supply. In this way, briny water being discharged from theRO subsystem is done so over a larger space, thereby reducing thelikelihood of the briny water corrupting the water supply. In thepresent context, briny water is any such water that, when reintroducedinto the supply from where it came, has a higher salt concentration thatof the surrounding supply. For example, if the saline water supply isthe sea, ocean or related body of water, the briny water would be thatproduced by the higher salinity RO subsystem discharge that is in turnplaced back into the body of water. Thus, one purpose of continuousoperation of the positioning mechanism associated with the RO subsystemduring the lowering and raising of the RO unit is that the brinyconcentrate leaving the RO unit is dispersed over a very large area andtherefore would not result in a significant difference in the salinityof the water through which is passes. An additional benefit is that thiswould prevent debris from accumulating on the surface of the membrane inthe RO unit.

Such a mechanism, may include a motor, winch and cable or relatedcoupling apparatus that together permit the subsystem to be movedthrough various depths of the saline water supply. In addition to beingfluidly connected to the RO unit, the container may include pressureregulating apparatus to control internal container pressure. Forexample, where an evacuation process is needed (such as prior tolowering the RO unit into the water), such pressure regulating apparatuscan be used to promote container evacuation, which in turn allows the ROwater storage container to fill completely without back pressure. Acontroller may be used to operate the various components of themechanism, as well as the water-gathering equipment of the RO subsystem.

According to another aspect of the present invention, a shipboard waterdesalination apparatus is disclosed. The apparatus includes an ROsubsystem with a saline water inlet, a purified water outlet and amembrane, a dehumidification subsystem and one or more storage tanks forthe collection of purified water. As with the previous aspect, themembrane allows preferential passage of water relative to salt in asaline water supply such that the water that passes through the membranehas a reduced salt content (as well as that of other contaminants)relative to that of the supply. The RO subsystem is further configuredas a passive device. In this way, pumps or related equipment that areneeded in conventional RO system to attain the high inlet pressuresnecessary to force the water through the membranes are not required, asa hydrostatic pressure of the saline water supply present at the salinewater inlet (due, for example, to at least the inlet of the apparatusbeing situated at a significant subsurface depth) is sufficient to passwater from the water supply through the membrane. Such passive pressuremay be produced from the system operating at depth where water is atmaximum density, such as where the water temperature is as close to 2°Celsius as possible. As with the previous aspect, continuous movement ofthe RO unit eliminates the accumulation of debris on the surface of theRO membrane that could otherwise cause problems in stationary RO unitsin use. Also as with the previous aspect, the dehumidification subsystemcan at least partially condense water present in an ambient air supply.Preferably, the dehumidification subsystem avoids the use of salinatedwater as a cooling agent to reduce the risk of subsystem contaminationand related fouling. In addition, using a cold water supply (such as thepurified water from the RO subsystem) as the source of the temperaturedifferential allows the dehumidification system to operate around theclock (i.e., experience a larger duty cycle) with greater efficiencybecause even at night (with a concomitantly cooler air temperature), thetemperature differential would still be enough to allow subsystemoperation, as the relatively cold temperature of the water accumulatedin a container or containers used in the RO subsystem helps provide atemperature differential that makes the dehumidification unit of thedehumidification subsystem work.

Optionally, the apparatus includes first and second positioningmechanisms, where the first is used with the RO subsystem to raise andlower the RO subsystem in the saline water supply, while the secondpositioning mechanism is used with the dehumidification subsystem suchthat the dehumidification subsystem can be preferentially orientedrelative to the ambient air supply. In one form, the second positioningmechanism can include motors and related gearing or related componentsnecessary to rotate or otherwise turn the dehumidification subsystem'sscreen, wall or related air-to-fluid heat exchanger. Such positioningmechanism may further include a controller (such as amicroprocessor-driven controller) to move the heat exchanger of thedehumidification subsystem such that the heat exchanger can beautomatically positioned to take best advantage of the prevailing winds.Such is preferable to having to reorient a ship (especially larger-classships) to take best advantage of such winds. The first positioningmechanism cooperative with the RO subsystem can be operated such that ifthe RO subsystem is mounted on a frame, sled or related support, thefirst positioning mechanism can be employed to raise and lower thesupport in the water to both attain the desired depth necessary toproduce the elevated hydrostatic pressures required of the membrane, aswell as keep the RO subsystem moving relative to the ambient salinewater supply. This latter movement, by virtue of its spreading the ROsubsystem effluent over a constantly-changing waterscape, is helpful inavoiding too large of a brine buildup in a single location adjacent theRO subsystem outlet. In one preferred form, the water collected from theRO and dehumidification subsystems is potable water that can later beconveyed (such as through piping, pumping, valving and associatedcontroller systems) to a remote storage facility, private or municipalwater supply or the like. Thus, for example, the controller can be usedto operate various compressors, vacuum pumps, valves or the like toensure proper conveyance of the purified water to a predeterminedstorage location. As with the previous aspect, the reduced salinity(i.e., purified) water coming from the RO subsystem can be used tocondense water vapor contained in the ambient air supply that comes intocontact with the dehumidification subsystem.

According to another aspect of the present invention, a method ofpurifying a saline water supply is disclosed. The method includesintroducing an RO subsystem comprising a saline water inlet, a purifiedwater outlet fluidly downstream of the inlet and a membrane disposedfluidly between the inlet and the outlet into the saline water supply toa sufficient depth to promote RO through the membrane. The method alsoincludes condensing at least some of the moisture present in a supply ofhumid air by a heat exchanger in a dehumidification subsystem. In thepresent context, humid air is any ambient air with a high enoughmoisture content to allow it to readily condense out when exposed to anaqueous heat exchange fluid (for example, cold purified water producedby the RO subsystem). As such, an ambient air supply with a relativehumidity of greater than 50% would be considered to be humid air, whilean ambient air supply with a relative humidity of around 10% would not.In addition to having a relative humidity of 50% or greater, it isdesirable to have the ambient air be at an air temperature of 70°Fahrenheit or greater. As such, tropical locations, which often exhibitboth high air temperatures and relative humidity, are advantageouslyused with the system of the present invention. Under such anarrangement, fresh (i.e., potable) water can be extracted from latentatmospheric humidity in hot, humid climates. The method further includescollecting purified water from the RO subsystem and the dehumidificationsubsystem in a storage tank.

Optionally, introducing the RO subsystem includes moving the ROsubsystem during its operation as a way to reduce brine concentration inthe adjacent water, in effect spreading out the briny water flowing outof the RO unit over a larger area. In one form, the condensing mayinclude using one or more of the saline water supply and the purifiedwater produced in the RO subsystem as a cooling liquid in the heatexchanger, which is preferably configured as a liquid-air heatexchanger. In a preferable option, the RO and dehumidificationsubsystems, as well as the storage tank, are mounted to or otherwiseintegrated onto a ship or related watercraft. As previously discussed,the storage tank may be made up of a series of separate tanks that canbe interconnected through appropriate piping, valving and pumpingapparatus. Placement of various storage tanks around the ship (such asaround the ship periphery) can be used with such apparatus toadvantageously promote ship balance by moving the stored potable waterbetween the various tanks. In another option, the heat exchanger can bepositioned, such as by rotating it relative to the ship or the supply ofhumid air to maximize heat exchange interaction.

In another option, the depth in the saline water supply is sufficient togive the local water supply enough driving force (by virtue of itselevated hydrostatic pressure) to pass the saline water supply throughthe membrane without the need to further pressurize the water supplythrough pumps or other mechanical, electromechanical or related means.In another option, the RO subsystem is introduced into the water supplyin a predetermined fashion to most economically reach the desiredpressurization levels at the RO subsystem membrane. For example, themethod may first include lowering the RO subsystem to a first depthsufficient to create at least 600 pounds per square inch pressure at themembrane, and then lowered to a depth sufficient to create about 1500pounds per square inch pressure at the membrane. The lowering rate ofthe RO subsystem between the condition where the pressure on themembrane is at least 600 pounds per square inch (psi) and the conditionwhere the pressure on the membrane is about 1500 psi is preferablybetween about 1 foot per minute and about 60 feet per minute. In a morepreferred form, the lowering rate is about 20 feet per minute. Inanother option, the purified water stored in the one or more storagetanks or the RO subsystem can be sampled, tested, analyzed or the liketo determine that it is of sufficient purity for its intended purpose.For example, if the water is being used for human consumption andrelated potable purposes, its salinity level (as well as that of otherpurity indicia) must meet certain threshold requirements. In this way,an operator may have the option of eliminating poor quality RO waterprior to it being brought aboard at all. Such sampling, testing,analyzing or the like may be part of a quality control program, and canbe further used to provide indicia of component (for example, membrane)malfunction or failure.

In another option, the containers used to collect the purified RO waterin the RO subsystem can be evacuated to a low pressure prior to beinglowered into the ocean or related saline water supply. In one form, thepressure can be reduced to less than about 1.47 psi to reduce oreliminate the back pressure in the container, thereby allowing it tofill more completely during operation without additional depressurizingbeing necessary during the cycle. In another option, cleaning steps maybe undertaken to eliminate or otherwise reduce the likelihood of foulingfrom contaminant build-up, such as salt, organic matter or the like. Inthis way, the purified water can be additionally treated to providedisinfection to eliminate microorganisms. Likewise, additionalfiltration devices can be used to remove suspended particulates. Aftersuch treatment, the purified water collected in the storage containercan then pumped out for subsequent use by the dehumidification system,storage in the shipboard storage tanks, or both.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description of the present invention can be bestunderstood when read in conjunction with the following drawings, wherelike structure is indicated with like reference numerals and in which:

FIG. 1 shows schematically a ship with an on-board water purificationsystem according to an embodiment of the present invention;

FIG. 2 shows details related to a submersible container and RO subsystemthat form part of the on-board water purification system of FIG. 1; and

FIG. 3 shows details related to an on-board dehumidification subsystemthat forms part of the on-board water purification system of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to FIG. 1, a ship 1 (such as a tanker) outfittedwith a potable water generation system according to an aspect of thepresent invention is shown. Ship 1 includes a dehumidification subsystem2, one or more purified water storage tanks 3, RO subsystem 4, a craneor winch 5 and piping 6 that can convey the cold water from the ROsubsystem 4 storage container to the dehumidification subsystem 2, andtanks 3. In a preferred form, the ship 1 is of a large-displacementvariety. For example, the ship 1 may be a minimum 40,000 ton capacity,appropriately designed or modified as shown for the purpose of potablewater production and storage. Such size must consider the ease withwhich ship 1 can navigate into and out of smaller ports and waterways,and it will be appreciated by those skilled in the art that differentsizes commensurate with these restrictions are within the scope of thepresent invention. As shown, ship 1 includes a hull 1A or related mainstructure that in turn provides either direct or indirect support forthe remaining features disclosed herein, such as docking stations 8.

The tanks 3 are preferably sterile, while portions of the piping 6 andrelated valving 7 selectively interconnects them to each other to enablethe shifting of the water between compartments to balance the floatationneeds of the ship 1 as potable water is accumulated. In a like manner,piping 6 and valving 7 can be used to convey cooling water and purifiedcondensate between the RO subsystem 4, the storage tanks 3 and thedehumidification subsystem 2. Docking stations 8 can be used to securethe RO subsystems 4 while the latter are on the topside of ship 1.

A set of vacuum pumps and compressors (neither of which are shown) areincluded on ship 1 to act as pressure and vacuum reservoirs that canenable continuous water production, as well as to shorten the length ofthe potable water production cycle. The vacuum pumps can be used toevacuate water containers 40 (discussed in more detail below), while thecompressors can be used as a means of forcing water out of thecontainers 40 through the piping 6 aboard the ship 1. Such devices,although not necessary, can shorten the time required to move thepurified water. The ship 1 can be propelled by conventional means (forexample, fossil fuels, nuclear reactor or the like), and preferably havesufficient fuel capacity to remain at sea collecting water for anextended period of time (such as at least one month).

Referring next to FIG. 2, the RO subsystem 4 (which may be procured froma well-known commercial source) includes one or more water containers 40that should be of design and of such construction as to withstand seadepths of up to 2500 feet or about 1500 psi pressure. While it will beappreciated that any appropriate shape may be used for container 40 (andall such shapes are deemed to be within the scope of the presentinvention), a generally spherical profile is recognized as providing thebest combination of structural efficiency and integrity under the highpressure conditions imposed by deep ocean submersion applications. Inone form, each of the containers 40 could be constructed of either metalor a reinforced composite or other appropriate structural material. Inone non-limiting form, each container 40 is about six feet in diameter,subject to the weight limitations and pressure factors previouslymentioned. In addition, the container 40 can be reinforced with internalspars 9 for added strength, as shown with particularity in the figure.As with tanks 3, the containers 40 perform a purified water storagefunction, the difference being that the tanks are generally affixed tothe ship 1, while the containers 40 can be lowered into the ocean inorder to achieve a measure of passive RO performance by virtue ofpressure differences across an RO membrane (not shown) from the oceandepths to the inside of the container 40.

The RO subsystem 4 also includes a membrane unit (also called an ROunit) 41 situated adjacent the container 40 and designed to enable theRO subsystem 4 to produce sufficient desalinated product water to fillthe container 40 in a relatively short amount of time. In onenon-limiting form each container 40 can be filled in approximately twohours. Purified water generated in the RO unit 41 is conveyed to itsrespective storage container 40 for temporary storage, such as untilsuch time as the container 40 can be brought to the ship 1 topside.

The container 40 should be of a size which can readily be raised fromocean depth by winch 5. The top of each of the spherical containers 40includes an eyelet, hook or the like with which winch 5 can lift andlower spherical containers 40 by cable 43. Operation of winch 5 can beperformed through the controller (not shown) to enable the winch 5 todraw in or let out cable 43 to raise and lower each of the containers 40at a preferred speed, which in some circumstances may need to be donerapidly, while in others more slowly. Together, winch 5, cable 43 andthe controller may make up a positioning mechanism for movement of theRO unit 41 and container 40. Similarly, the controller can be used tomanipulate each of the containers 40 into appropriate seating withintheir respective docking station 8. In one form, the containers 40 canbe lowered into the water to a first depth. For example, each container40 can be lowered to about a 1000 foot depth, which should be sufficientto create approximately 600 psi at an inlet (also known as an intake)42A of RO unit 41. Once it has attained the sufficient depth orpressure, the container 40 can continue to be lowered, now at acontrolled rate, such as between about 1 and 60 feet/minute. In onepreferred form, the container 40 can be lowered at about 20 feet/minute.Such lowering continues until a pressure sufficient to enable the ROunit 41 of the RO subsystem 4 to operate is attained. For example, adepth of 2500 feet should generally be sufficient to produce about 1500psi at the inlet 42A of RO unit 41. The inventor has discovered thatcontinuous operation of the RO subsystem 4 as it is being both loweredand raised avoids brine concentration at the inlet 42A of the RO unit41, and greatly reduces environmental concerns with brine dispersalsince the concentrate will be dispersed over a much broader area.Preferably, the RO unit 41 is fitted with all necessary screens,filters, pretreatment apparatus or the like (none of which are shown)necessary for prolonged deep sea use. Salt and other contaminants thatget filtered out by membrane pass out of the RO unit 41 through outlet42B.

The top of the container 40 is equipped with multiple pipes 6A, 6B, eachhaving respective electric closure solenoid valves 10A and 10B andaccompanying vacuum seals (not shown). These pipes 6A, 6B connect the ROsubsystem 4 to the storage tanks 3 to maximize flow volume into thecontainer 40. To achieve this, they can be used to evacuate residual airfrom the container 40 prior to the container 40 being lowered into theocean or related body of water. The evacuation helps to relieve backpressure, as well as to allow for maximum filling of the container 40.The pipes 6A and 6B can also be used to remove water from the container40 through an appropriate hose (not shown) that can be used to connect ashipboard suction pump to the pipe 6A which extends into the bottom ofthe container 40 to allow siphoning out the water contained therein. Inan alternate form, a compressor (not shown) can be fluidly connected tothe short pipe 6B on the top of the container 40 to exert downwardpressure on the water in container 40 to help force it up through thepipe 6A. In this way, the pipes maintain sufficient pressure and vacuumon the containers 40 throughout the water production and retrievalprocesses. Of the two pipes 6A and 6B, pipe 6A extends lower, reachingnearly to the bottom of the container 40 to allow for the removal ofpurified product water that is delivered to the container 40 from theadjacent RO unit 41 through piping (not shown). As stated above, valve10A can be used to selectively close off the open end of pipe 6A to theremainder of the piping 6 that is used to convey the purified water. Theother pipe 6B terminates in an opening near the top of the inside of thecontainer 40, and can be used to maintain proper container pressure. Aswith pipe 6A, pipe 6B can be fitted with an automated closable valve10B.

In addition to the RO subsystem 4, the ship 1 has a large capacitydehumidification subsystem 2. As shown with particularity in FIG. 3, thedehumidification subsystem 2 includes one or more relatively largesurface area ambient air capture screens 20 that can be fluidly coupledthrough piping 7 to one or more potable water storage tanks 3 such thatcondensate from the dehumidification subsystem 2 is placed in thepotable water storage tanks 3. Capture screen 20 is preferably equippedwith hydraulic or mechanical powered devices (such as motor 22) that canposition the capture screen(s) 20 to maximize the utilization ofprevailing winds that blow across the ship 1. A mounting base 24 allowsrotation of capture screen 20 through an appropriate mechanism, such asball bearings 26 that are mounted to base 24. This arrangement allows aminimum of 180° rotation in response to motor 22. Cooling water, whichis used as a condensing agent for capture screen 20, can be introducedfrom the cold water from the containers 40 of the RO subsystem 4 throughpiping 6C. In a likewise fashion, potable condensate can be removed fromcapture screen 20 through piping 6P to be delivered to one or more ofthe storage tanks 3.

In one proposed (although not necessary) mode of operation, ship 1 wouldbe located in a tropical environment, such as the Gulf of Mexico.Locations such as this are desirable because the water has sufficientdepth (i.e., approximately 2500 feet) to allow the lowering of thecontainers 40 of the RO subsystem 4, although it will be appreciated bythose skilled in the art that any saltwater environment where such waterdepth and ambient air conditions exist is equally usable. Prior toimmersion of the containers 40 and RO unit 41 of the RO subsystem 4 intothe sea, ocean, bay, gulf or related body of water, the container 40 isevacuated to a significant vacuum, such as in a manner discussed above.In one preferred form, the pressure inside the container 40 is reducedto about 1.47 psi or less (compared to approximately 14.7 psi forstandard atmospheric pressure). A pressure indicator on ship 1 can beused to measure pressure in container 40 to indicated how much pressurelowering is required.

Moreover, the rates of RO subsystem 4 ascent and descent can be variedin order to correlate with the capacity of the RO subsystem 4 to processthe quantity of water needed to fill the container 40. In one form, thecontainer 40 could be about half filled with product water, at whichtime the winch 5, cable 43 and container 40 can cooperate to raise thecontainer 40 back toward the surface at about a predetermined ascentspeed. In one form, such speed could be about 20 feet/minute. When theRO subsystem 4 reaches the 1000 foot depth level, the solenoid valves10A, 10B connecting the container 40 to the RO subsystem 4 will beclosed, at which time the containers 40 are pulled to the surface asrapidly as possible. In this way, the total length of the RO cycle isreduced, and the operation of the RO process only takes place duringthose times where the container 40 of the RO subsystem 4 below the depthnecessary to generate the pressures needed. Referring again to FIG. 2,when the container 40 reaches the surface of the water, an on-boardpressure source (such as from water handling subsystem 30) is connected(via hose, for example) to the upper pipe 6B on top of the container 40.Another connection, this time to lower pipe 6A that extends almost tothe bottom of the container 40, can also be made to the water handlingsubsystem 30. Both valves 10A and 10B are then opened so that pressurefrom the water handling subsystem 30 is applied to cause the colddesalinated water to flow out of the containers 40 to the shipboardmoisture dehumidification subsystem 2 (where it can act as a condensingagent for moist air passing across one or more capture screens 20, andfrom there, to the shipboard storage tanks 3. As discussed above, eachof the containers 40 of the RO subsystem 4 can be sampled, such as forchloride ion content. Likewise, the inlet 42A of the RO unit 41 can beinspected and serviced, if needed.

Regarding operation of the dehumidification subsystem 2, the temperaturedifferential between the cold RO water in the container 40 and the warmtropical air flowing through the dehumidification subsystem 2 willresult in production of substantial quantities of pure water condensate.A trough 24 situated beneath the dehumidification subsystem 2 willfunnel the accumulated condensed water vapor out of the dehumidificationsubsystem 2 so it can then be pumped into the water storage tanks 3 tobe joined up with the RO water from the RO subsystem 4 that was used tocondense the airborne water vapor that was captured by thedehumidification subsystem 2.

Ship 1 may be equipped with numerous RO subsystems 4 so that theimmersion process of the multiple containers 40 and accompanying ROunits 41 may be sequenced to provide around-the-clock production ofpotable water. Likewise, connection of the various containers 40 to thedehumidification subsystem 2 ensures continuous water processing,although it may be that more dehumidification of the ambient air ispossible in the daylight hours, where the temperature difference betweenthe air and the RO water is greatest. Furthermore, when the holds ofship 1 are filled and the ship 1 is situated in a port or relateddocking facility, suitable pumping and related water conveying means canbe fluidly coupled to the ship 1 to facilitate delivery of the purifiedwater to the port or other land-based water transfer or storing station.Multiple ships 1 may be employed to ensure substantially continuousoperation.

According to a particular aspect of the present invention, if one of thesubmergible water containers 40 that is used to hold the product ROwater is open to ambient air temperature and pressure while on the ship1 prior to being submerged, the entering air would be at about 30degrees Celsius and 15 (more particularly, 14.7) psi. If that watercontainer 40 is then lowered to a significant ocean depth (for example,around 1000 feet as discussed herein, or greater), the change intemperature from the ambient conditions discussed above down to a depthwater temperature of 2 degrees Celsius will cause a significantreduction in pressure within the container 40 in accordance with idealgas laws. In such a scenario, the air vent/valve that permitted theambient air to enter container 40 while topside is closed beforecontainer 40 is lowered into the ocean or related saline water supply inorder to isolate the air contained therein and allow the subsequentformation of a vacuum upon reduction of the temperature of the trappedair due to exposure to the colder subsurface water. The valve connectingthe RO unit to the sphere is also closed until such time as the ROprocess begins at ocean depth.

Accordingly the RO product water will be able to enter the container 40passively (i.e., without the need for pumping or evacuation devices) asthe pressure of the water emerging downstream of the RO unit 41 and theback pressure within the fluidly-connected container 40 will both below. After the container 40 reaches such a depth sufficient for the ROprocess to begin, it and the RO unit 41 can be lowered in order to flushany concentrated brine from the membrane surface of the RO unit 41,thereby allowing even more incoming water pressure to the unit. As aresult, the container 40 will fill to a significant portion (i.e., atleast 50%) of its volumetric capacity before the pressure within equalsthe pressure of the water emerging from the RO unit 41. When thisequilibrium has been reached, the container 40 could be winched to thesurface (such as through winch 5) and emptied through piping 6 to theshipboard moisture dehumidification subsystem 2 to condense outadditional quantities of pure water from the moist ambient air availableat the surface. Thus, the desalinated water from the RO unit 41, as wellas the additional water obtained by the moisture dehumidificationsubsystem 2 are both then piped into storage tanks 3 as discussedpreviously.

In a variation on this approach as discussed above, the air resident incontainer 40 can be evacuated (for example, down to a level of about1.47 psi) prior to being lowered into the saline water supply. Thispressure is readily attained with conventional commercial vacuum pumps(not shown) as a way to evacuate water containers 40. In this case, theback pressure that develops in the closed, evacuated container 40 beinglowered into the saline water supply will be extremely low due to boththe evacuation of the residual air prior to being lowered and theinfluence of the lower water temperature at ocean depth. In suchcircumstance, it should be possible to fill the container 40 to at leastabout 90% of its volumetric capacity before pressure equals that of theincoming desalinated water from the RO unit 41. This increase in thevolumetric capacity of the product sphere from about 50% without priorevacuation to at least 90% with prior evacuation is economicallydesirable, as it may decrease the number of raising and lowering stepsof the container 40 and RO unit 41 to acquire the same amount of potablewater.

In these above configurations, a ship 1 or related watercraft can beused for producing purified water by including a passive RO subsystem 4with a saline water inlet, outlet and membrane as discussed above. Inaddition, a submergible water container 40 is cooperative with the ROsubsystem 4; the container 40 defines an internal evacuatable regionwhere one or both of a lower-temperature trapped air mass and aprevious-introduced vacuum can be employed to allow more desalinatedwater produced by the RO unit 41 to enter and be stored in the container40 by operation of their inherent pressure differential. Suchconfigurations and approaches are associated with pre-evacuation of thecontainer 40 before it is lowered into to the depths of the saline watersupply.

While certain representative embodiments and details have been shown forpurposes of illustrating the invention, it will be apparent to thoseskilled in the art that various changes may be made without departingfrom the scope of the invention, which is defined in the appendedclaims.

1. A watercraft for producing purified water, said watercraftcomprising: a passive reverse osmosis subsystem comprising a salinewater inlet, a saline water outlet fluidly downstream of said inlet anda membrane disposed fluidly between said inlet and said outlet andconfigured to allow preferential passage of water relative to salt in asaline water supply passed therethrough; a submergible water containerin fluid communication with said reverse osmosis subsystem to receivepurified water that has passed through said membrane, said submergiblewater container defining an evacuatable region such that a vacuum may beselectively formed therein; a passive dehumidification subsystemconfigured to use said purified water in order to condense at least aportion of water contained in an ambient air supply that comes inthermal contact with said purified water present in said passivedehumidification subsystem; at least one purified water storage tankconfigured to receive said purified water from said submergible watercontainer and said condensed water from said dehumidification subsystem;and a hull for supporting said reverse osmosis subsystem, saidsubmergible water container, said dehumidification subsystem and said atleast one tank.
 2. The watercraft of claim 1, wherein said evacuatableregion becomes at least partially evacuated by taking advantage of atrapped ambient air supply that is introduced into said submergiblewater container at a higher temperature and then thermally exposed to alower temperature associated with said submergible water container beingsubmerged in said saline water supply.
 3. The watercraft of claim 1,wherein said evacuatable region becomes at least partially evacuated bycreating at least a partial vacuum therein prior to operation of saidpassive reverse osmosis subsystem.
 4. The watercraft of claim 3, whereinsaid at least a partial vacuum is no greater than about 1.47 psi.
 5. Thewatercraft of claim 1, further comprising a winch configured to movesaid submergible water container and said reverse osmosis subsystemthrough various depths of the saline water supply.
 6. The watercraft ofclaim 1, further comprising a controller configured to regulate raisingand lowering of said submergible water container with said winch.
 7. Thewatercraft of claim 1, wherein said passive dehumidification subsystemcomprises an air capture device configured to receive therethrough atleast a portion of the ambient air supply.
 8. The watercraft of claim 7,wherein said air capture device comprises an air capture screen.
 9. Thewatercraft of claim 1, wherein said dehumidification subsystem ispositionable relative to the ambient air supply such that the amount ofthe ambient air that interacts with said air capture device ismaximized.
 10. A method of purifying a saline water supply, said methodcomprising: at least partially evacuating a submergible water container;fluidly coupling said submergible water container to a reverse osmosisdevice; submerging said reverse osmosis device into the saline watersupply to a sufficient depth to promote passive hydrostatic reverseosmosis therethrough; collecting purified water from said reverseosmosis device into said submergible water container; exchanging heatbetween said collected purified water and at least a portion of themoisture present in a supply of ambient humid air such that at least aportion of said moisture is condensed; and placing said collectedpurified water and said condensed moisture into at least one potablewater storage tank.
 11. The method of claim 10, wherein said exchangingheat occurs in a passive dehumidification subsystem comprising a heatexchanger.
 12. The method of claim 10, further comprising mounting saidreverse osmosis device, said passive dehumidification subsystem and saidstorage tank on a watercraft.
 13. The method of claim 10, wherein saidat least partially evacuating said submergible water container isachieved by trapping a supply of the ambient humid air in saidsubmergible water container prior to said submerging said reverseosmosis device into the saline water supply such that a lowering oftemperature in the trapped ambient humid air caused by said submergingcauses a lowering of pressure inside said submergible water container.14. The method of claim 10, wherein said at least partially evacuatingsaid submergible water container is achieved by introducing a partialvacuum in said submergible water container such that upon saidsubmerging, a pressure differential relative to said reverse osmosisdevice exists.
 15. The method of claim 14, wherein said introducing apartial vacuum is created by establishing a pressure connection betweensaid submergible water container and a ship-based vacuum pump andoperating said pump to withdraw at least a portion of air resident insaid submergible water container.
 16. The method of claim 15, whereinsaid introducing a partial vacuum comprises reducing the pressure insaid submergible water container to not more that about 1.47 psi.
 17. Amethod of operating a watercraft to purify a saline water supply, saidmethod comprising: configuring said watercraft to comprise a reverseosmosis device, a submergible water container and a passivedehumidification device such that said reverse osmosis device is influid communication with said submergible water container and saidsubmergible water container is in heat exchange communication with saidpassive dehumidification device; at least partially evacuating saidsubmergible water container; submerging said reverse osmosis device intothe saline water supply to a sufficient depth to promote passivehydrostatic reverse osmosis therethrough; collecting purified water fromsaid reverse osmosis device into said submergible water container;conveying said collected purified water from said submergible watercontainer to said passive dehumidification device such that at least aportion of the moisture present in a supply of ambient humid air iscondensed through thermal interaction between the supply of ambient airand said conveyed purified water; and placing said conveyed purifiedwater and said condensed moisture into at least one potable waterstorage tank.
 18. The method of claim 17, wherein said at leastpartially evacuating said submergible water container is achieved bytrapping a supply of the ambient humid air in said submergible watercontainer prior to said submerging said reverse osmosis device into thesaline water supply such that a lowering of temperature in the trappedambient humid air caused by said submerging causes a lowering ofpressure inside said submergible water container.
 19. The method ofclaim 17, wherein said at least partially evacuating said submergiblewater container is achieved by introducing a partial vacuum in saidsubmergible water container such that upon said submerging, a pressuredifferential relative to said reverse osmosis device exists.